The importance of differentiating and identifying individuals based on biological samples with a high degree of efficiency and accuracy is presented in various contexts. For example, the need for accurate means of identification is of increasing importance in law enforcement as it may be critical to link an individual to a forensic sample, such as blood, tissue, hair, saliva, or the like.
Many methods are known for identifying individuals or biological samples obtained from such individuals. For example, blood typing is based on the existence of antigens on the surface of red blood cells. The ABO system relates to four different conditions with respect to two antigens, A and B. Type A individuals exhibit the A antigen; Type B individuals exhibit the B antigen; Type AB individuals exhibit both the A and B antigens; and Type O individuals exhibit neither the A nor the B antigen. By analyzing a sample of a person's blood, it is possible to classify the blood as belonging to one of these blood groups. While this method may be used to identify one individual out of a small group of individuals, the method is limited when the group of individuals is larger because no distinction is made between persons of the same blood group. For example, the distribution of the ABO blood groups in the U.S. is approximately 45% O, 42% A, 10% B, and 3% AB. Tests based on other blood group antigens or isozymes present in body fluids suffer from the same disadvantages as the ABO blood typing tests. These methods may exclude certain individuals, but cannot differentiate between members of the same blood group.
A variety of immunological and biochemical tests based on genetics are routinely used in paternity testing, as well as for determining the compatibility of donors and recipients involved in transplant or transfusion procedures, and also sometimes as an aid in the identification of humans and animals. For example, serological testing of proteins encoded by the human leukocyte antigen (HLA) gene locus is well known. Although a good deal of information is known concerning the genetic makeup of the HLA locus, there are many drawbacks to using HLA serological typing for identifying individuals in a large group. Each of the HLA antigens must be tested for in a separate assay, and many such antigens must be assayed to identify an individual, an arduous process when identifying one individual in a large group.
In the past decade, DNA-based analysis methods, such as restriction fragment length polymorphisms (RFLPs) and polymerase chain reaction (PCR) have rapidly gained acceptance in forensic and paternity analyses for matching biological samples to an individual. RFLP techniques are problematic, however, due to the need for relatively large sample sizes, specialized equipment, highly skilled technicians, and lengthy analysis times. For forensic applications there is often not enough sample available for this type of assay, and in remote areas the necessary equipment is often not available. In addition, the cost and length of time required to performed this technique may hinder a criminal investigation. Moreover, the cost of RFLP analysis may be prohibitory if screening of many samples is necessary. PCR techniques have the advantages over RFLP analysis of requiring much smaller sample sizes and permitting more rapid analysis, but they still require specialized equipment and skilled technicians, and they are also expensive.
Antibody profiling is an identification technique that has many advantages over conventional DNA-based analysis methods. For example, antibody profiling methods provide increased speed and ease of use and decreased costs in comparison to conventional DNA based analysis. Current antibody profiling methods for identifying individuals utilize an undefined mixture of proteins.
U.S. Pat. No. 4,880,750 and U.S. Pat. No. 5,270,167 each disclose antibody profiling as a method that purportedly overcomes many of the disadvantages associated with DNA analysis. The antibody profiling method is based on the discovery that every individual has a unique set of antibodies present in his or her bodily fluids. R. M. Bernstein et al., Cellular Protein and RNA Antigens in Autoimmune Disease, 2 Mol. Biol. Med. 105-120 (1984). Such antibodies, termed “individual-specific antibodies” or “ISAs,” were found in blood, serum, saliva, urine, semen, perspiration, tears, and body tissues. A. M. Francoeur, Antibody Fingerprinting: A Novel Method for Identifying Individual People and Animals, 6 Bio/technology 821-825 (1988). The ISAs are not associated with disease and are thought to be directed against cellular components of the body. Individuals are born with an antibody profile that matches the mother's antibody profile. T. F. Unger & A. Strauss, Individual-specific Antibody Profiles as a Means of Newborn Infant Identification, 15 J. Perinatology 152-155 (1995). An individual's antibody profile gradually changes, however, until a stable unique pattern is obtained by about two years of age. It has been shown that even genetically identical individuals have different antibody profiles. An individual's profile is apparently stable for life and is not affected by short-term illnesses. A. M. Francoeur, supra. Few studies have been conducted on individuals with long-term diseases. Preliminary results, however, indicate that, although a few extra bands may appear, the overall pattern remains intact. This technique has been used in the medical field to track patient samples and avoid sample mix-ups. In addition, the technique has been used in hospitals in cases where switching of infants or abduction has been alleged.
WO 97/29206 discloses a method for identifying the source of a biological sample used for diagnostic testing by linking diagnostic test results to an antibody profile of the biological sample. By generating an antibody profile of each biological sample, the origin of the biological sample is identified.
Assays are also available that use specific nucleic acid probes or other biological molecules attached to surfaces such as glass, silicon, polymethacrylate, polymeric filters, microspheres, resins, and the like. In a configuration where the surface is planar, these assays are sometimes referred to as “biochips.” Initially, biochips contained nucleic acid probes attached to glass or silicon substrates in microarrays. These DNA or RNA chips are made by microfabrication technologies initially developed for use in computer chip manufacturing. Leading DNA chip technologies include an in situ photochemical synthesis approach, P. S. Fodor, 277 Science 393-395 (1997); U.S. Pat. No. 5,445,934; an electrochemical positioning approach, U.S. Pat. No. 5,605,662; depositing gene probes on the chip using a sprayer that resembles an ink-jet printer; and the use of gels in a solution-based process. Arrays of other types of molecules, such as peptides, have been fabricated on biochips, e.g., U.S. Pat. No. 5,445,934.